BAGHDAD — A suicide bomber killed 52 people among a crowd of police recruits in Saddam Hussein’s hometown Tuesday, shattering a two-month lull in major attacks and spurring calls to keep the U.S. military in Iraq beyond 2011.

It was the second time in three days that efforts to bolster Iraqi police and army soldiers have backfired. The violence underscores persistent gaps in the security forces’ ability to protect the country, despite seven years and $22 billion in training and equipment provided by the U.S.

In an all-too-familiar scene, the suicide bomber joined hundreds of recruits waiting outside a police station in Tikrit to submit applications for 2,000 newly created jobs — a plum, if risky, opportunity in a country with an unemployment rate as high as 30 percent.

At about 10 a.m., the bomber detonated his explosives-packed vest. The blast left blood, flesh and clothing sprayed across the dirt ground. A nearby car was peppered with shrapnel. In addition to the 52 dead, 150 people were wounded, authorities said.

“I saw wounded people running in my direction calling for help and asking me to take them to the hospital immediately,” said taxi driver Abdul-Hamid Mikhlaf. “I saw several bodies on the ground as the policemen started to shoot in the air.”

Loudspeakers from the city’s mosques implored people to donate blood for the wounded. A grenade that had not exploded was found near the scene.

Prime Minister Nouri al-Maliki blamed the strike on terrorists who he said have continued their history of “shedding the blood of innocent people and targeting young brave who came to serve their country and defend its security and stability.”

“The frequency of these heinous crimes with the same style indicate a blemish on, or clear negligence by the responsible authorities,” al-Maliki said. “We will follow up the matter with all seriousness in order to determine negligence … and the cause of the occurrence of this painful tragedy.”

Questions immediately arose over what measures security forces had taken to prevent yet another such attack.

One recruit said the job applicants were frisked before they entered the station’s yard.

“We were waiting in the line to enter the police station yard after being searched when a powerful explosion threw me to the ground,” said Quteiba Muhsin, whose legs were fractured in the blast. “I saw the dead bodies of two friends who were in the line.

“I am still in shock.”

A statement posted on a militant website by the Islamic State of Iraq, an al-Qaida front group, praised the bombing as a “suicide martyrdom” but stopped short of claiming responsibility. Tikrit, located 80 miles (130 kilometers) north of Baghdad, is the capital of Sunni-dominated Salahuddin province, and the city sheltered some of al-Qaida’s most fervent supporters after the 2003 U.S.-led invasion ousted Saddam.

Local politicians blamed al-Qaida.

“This is evidence that the entire Iraqi nation is being targeted. It is a clear failure by the security forces, and I expect there will be more attacks,” said Falah al-Naqaeeb, a lawmaker from Salahuddin who has been nominated by the Sunni-dominated Iraqiya political coalition to be Iraq’s next defense minister.

Al-Naqaeeb said attacks likely will spike if U.S. forces leave Iraq at the end of the year.

“The Iraqi security forces need the expertise from the Americans,” he said. “They shouldn’t be in a hurry with the withdrawal. And the Iraqi government should reconsider the withdrawal date because our forces are not yet ready.”

The Dec. 31 withdrawal deadline is part of a security agreement between Baghdad and Washington from which neither side has budged so far. Moreover, an attack by an Iraqi army soldier that killed two U.S. troops Saturday during a training drill in the northern city of Mosul casts further doubt that the military would be willing to stay.

A senior U.S. Embassy official this week maintained that the year-end deadline will stand until the Iraqi government explicitly asks for it to be extended. If a request is made, President Barack Obama would have to approve it amid a hostile American political climate as he eyes re-election in 2012.

“There is no discussion right now on that issue, because there is no request,” the Embassy official told reporters in a briefing where he agreed to talk on condition of anonymity to discuss diplomatic issues more candidly.

Douglas Ollivant, who oversaw Iraq issues at the National Security Council in 2008-09 after two U.S. Army tours here, said it’s still too soon to judge the ability of Iraqi forces.

“Objectively speaking, can we help them more if we stay longer? Obviously, yes,” said Ollivant, now a contract adviser to NATO forces in Afghanistan. “But they have to make their own decisions.”

The performance of Iraqi forces has varied wildly throughout their training. The army is generally seen as competent, while police forces are uneven depending largely on their location, funding and support. Meanwhile, local militias such as the Sunni-run Sons of Iraq and the Kurdish peshmerga were given little equipment and training until they recently began to be integrated into police and army ranks.

Insurgents have long found recruitment centers a favorite target, taking advantage of lax security measures just outside protective barriers at police and army stations and the confusion caused by desperate jobseekers scrambling for work.

A similar strike on an Iraqi recruitment center and army headquarters in central Baghdad last August left 61 dead and 125 wounded. Two weeks later, militants attacked the same building again, detonating a car bomb and trying to shoot their way in, killing eight and wounding 29.

Tuesday’s bombing followed a two-month lull that saw mostly small-scale bombings and shootings across Iraq instead of spectacular violence.

It was the deadliest attack since Nov. 2, when rapid-fire bombings and mortar strikes killed 76 people and wounded more than 200 in at least 13 Baghdad neighborhoods in a demonstration of insurgents’ ability to carry out coordinated strikes from one side of the capital to the other.